Chemical Education Today
Letters On the Stereochemistry of “Natural”␣Amino Acids In the first issue of 2000, I enjoyed the intriguing article by S. H. Leung on the common names of naturally occurring and synthetic compounds (J. Chem. Educ. 2000, 77, 48–49). Despite the care the author took in retrieving and reporting the derivation for a lot of names, in my opinion a major correction should be introduced in Table 1, where the systematic names for amino acids are given. Assuming that this list concerns “natural” amino acids (they are referred to as “biologically important” in note a) they all belong to the L steric series, with the obvious exception of glycine. Thus, the correct stereochemical descriptor for the absolute configuration at the α-carbon atom should be (S) for all of them but cysteine (and cystine, of course). In fact, since HSCH2– has a higher priority than HO2C–, L-cysteine is an exception to the generalization that all natural amino acids have (S) configuration at their α-carbon atom: actually, L-cysteine has (R) configuration.
The author replies: I thank Giovanni Lentini for pointing out my error in the configuration assignment for L-cysteine. The natural amino acid L-cysteine should have the (R) configuration. I apologize for the mistake. Thank you. Sam Leung Department of Chemistry Washburn University Topeka, KS 66621
Giovanni Lentini Dipartimento Farmaco-Chimico, Facoltà di Farmacia 70125 Bari, Italy
[email protected] 558
Journal of Chemical Education • Vol. 79 No. 5 May 2002 • JChemEd.chem.wisc.edu
